Relatively little is known about the physiological factors that mediate the memory deficits seen with sleep deprivation (SD). This proposal aims to investigate the sequences of SD for the memory process and to determine their neurophysiological substrates. Subjects will undergo fMRI, both after a normal night of sleep and after SD, while memorizing words being presented both visually and auditorally. The change in signal intensity between the "stimulation" and "no-stimulation" conditions will be measured. It is hypothesized that SD will enhance cerebral figure- ground activation, manifested as an increase in the percent change in the signal intensity of modality-specific regions after SD, cared to after normal sleep. After imaging, subjects will be given both explicit and implicit memory tests. It is expected that explicit memory will be impaired following SD. If implicit memory is also impaired, the encoding process will be implicated as sensitive to the effects of SD. If instead, implicit memory remains intact after SD, the retrieval process will be implicated. This project will answer questions regarding the neurophysiolcgical basis for the memory deficits seen with SD, holds implications for the field of "sleepiness and performance," and may bring to light a new technique for studying the consequences of sleep loss and SD.